Apparatus for bonding together metal sheets by explosive welding

ABSTRACT

Apparatus for explosively welding two metal layers together by providing one layer with a carrier of open-celled foamed plastic material and depositing explosive salt in crysta state on the walls of the cells of such foamed material.

United States Patent [72] lnventor Per lngemar Persson Huddinge, Sweden [21] Appl. No. 860,280 [22] Filed Sept. 23, 1969 [45] Patented Nov. 30, 1971 [73] Assignee Nitro Nobel AB Gyttorp, Sweden [32] Priority Sept. 23, 1968 [33] Sweden [31] 12802/1968 [54] APPARATUS FOR BONDING TOGETHER METAL SHEETS BY EXPLOSIVE WELDING 4 Claims, 1 Drawing Fig.

[52] U.S.C1 161/160, 29/470.1, 29/486, 149/3, 149/15 [51] lnt.C1 B321) 3/26 [50] Field oISearch 149/3, 14,

[56] References Cited UNITED STATES PATENTS 1,671,792 5/1928 Stoops 149/3 X Kropa et al. Fuller Campbell Cowan et a1.

Vincent et a1.

Schroter et a1.

Chudzik Stark FOREIGN PATENTS Great Britain Primary Examiner-John F. Campbell Assistant Examiner- Ronald .1. Shore AnorneysA. Yates Dowell and A. Yates Dowell, Jr.

156/77 156/79 UX 156/77 X 29/421 UX 156/78 156/79 X 29/421 X 149/14 X ABSTRACT: Apparatus for explosively welding two metal APPARATUS FOR BONDING TOGETHE R'METAL SHEETS BY EXPLOSIVE WELDING This invention relates to a method and an arrangement for bonding together metal sheets by means of explosive welding.

More particularly this invention relates to a method for bonding together metal sheets'by means-of explosive welding which means that a layer of explosive is applied to the exterior face of at least one of the sheets and that by detonation of said explosive so powerful a pressure or shock is produced between the sheets that these are metallically welded together. This method is described e.g. in the Swedish Pat. specification 183,172. On the other hand, it is known to distribute an explosive such as pentaerythritol-tetranitrate (PETN) in a carrier of a porous material with open cells such as foamed plastic, for example. The explosive is deposited in the pores in the fonn of crystals and the quantity per unit volume of the carrier is little.

One main object of the invention is to provide a method, which combines the advantages of both methods, while avoiding the drawbacks inherent to each of them in order to obtain perfect explosively welded products.

Another object of the invention is to utilize a carrier of the said type for bonding together thin metal sheets. The invention is substantially characterized therein that placed on the one metal sheet is a disk of a porous substance having open cells, such as foamed plastic, in which particles of an explosive are distributed and in this state are brought to detonate. Due to the fact that the density of explosive per unit volume is little, it is avoided that the metal surface hit by the detonation shock wave is damaged or deformed even if the plate is thin and of so soft material as aluminum, for example. An embodiment particularly suitable for carrying out the method is characterized thereby that the disk on its one side is connected with the one metal sheet to constitute a prefabricated unit.

Further objects and advantages of the invention will become apparent from the following description considered in connection with the accompanying drawing, which forms part of this specification and in which one embodiment of the invention is illustrated in a perspective view.

Referring now to the drawing, reference numeral 10 denotes a disk of foamed plastic such as polyethylene, for example, having a low-volume weight such as 10 to 40 grams per cubic decimeter, for example. Deposited inside this disk are crystals of PETN as will b'e'described nearer more below. A thin sheet 12 of a metal such as aluminum is united with the disk 10 to form a commercial unit. The sheet 12 may have a thickness from a foil or film up to mm. On its opposite side, the disk is suitably covered by a reinforcing layer 14, e.g. made of hard fiber material and intended to prevent the thin metal sheet from becoming bent or deformed in other manner during transportation and the like. The joining together of the parts l0, l2, 14 may be brought about by means of an adhesive in a manner known per se.

The disk 10 of foamed plastic has open cells, the walls of which are elastic so that the disk may be squeezed up like a sponge to regain its original volume upon relief from the squeezing pressure.

Explosive in the form of nonphlegmatized, dried PETN is dissolved in acetone to a concentration of e.g. 15 percent of the explosive. The disks of foamed plastic are then immersed into the solution and thereafter into cold water which results in that the explosive is deposited in crystal state on the walls of the pores of the foamed plastic, because the substance is nonsoluble in water.

The dissolution of the explosive in the acetone may be effected at room temperature. The disk of foamed plastic may be kept immersed in said solution during about 3 minutes. Without being squeezed, the disk is then kept immersed in water during about 10 minutes. As an alternative, it may be squeezed up after having been kept immersed below the water surface during a shorter time such as 1 minute.

By raising the temperature of the solution of PETN above room tem erature, such as between 30 and 50 C., the disk of foamed p astic becomes capable of absorbing a greater quantity of explosive such as 0.06 to 0.08 grams per cubic centimeter. According to tests, the speed of detonation, which in turn is dependent on the density of the explosive in the foamed plastic, was increased thereby to more than 1,700 meters, such as up to 1,900 meters per second.

The thickness of the disk of foamed plastic may be from 5 to 40 millimeters. With a disk thickness of 20 millimeters, aluminum sheets of 3 millimeters could be bonded together with plates of steel and copper.

According to the invention, the metal sheet 12 with the porous explosive containing disk 10 and the reinforcing layer 14 can be produced and sold as a product or piece goods ready for immediate use. It is thus only necessary to cut out a piece of this piece goods, which suits to the shape of the metal sheet 16 with which the metal sheet 12 is to be bonded together.

The initiation of the explosive is effected from one side edge of the disk by means of an electrically operated ignition device or detonator (not shown) in a manner known per se.

The disk of foamed plastic is to be thicker than the metal sheet 12 by many times, such as at least five times, and preferably so many as 20 to I00 times.

While one more or less specific embodiment of the invention has been shown and described, it is to be understood that this is for purpose of illustration only and that the invention is not to be limited thereby, but its scope is to be determined by the appended claims.

What is claimed is:

1. Apparatus for explosively welding a first metallic layer to a second metallic layer comprising a first relatively thin metallic layer having first and second surfaces, a carrier of opencelled foamed plastic material connected to said first surface of the thin metallic layer, explosive salt in crystal state deposited on the walls of the cells of said foamed material, so that when said second surface of the thin metallic layer is placed on the second layer and the explosive salt crystals are ignited, said first layer will be welded to the second layer.

2. The structure of claim 1 in which the foamed material absorbs approximately 0.06 to 0.08 grams of explosive crystals per cubic centimeter of said carrier.

3. The structure of claim 1 in which said explosive salt is pentaerythritol-tetranitrate.

4. The structure of claim 1 in which said carrier is adhesively bonded to said first surface.

t t i i 

2. The structure of claim 1 in which the foamed material absorbs approximately 0.06 to 0.08 grams of explosive crystals per cubic centimeter of said carrier.
 3. The structure of claim 1 in which said explosive salt is pentaerythritol-tetranitrate.
 4. The structure of claim 1 in which said carrier is adhesively bonded to said first surface. 